Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several small-sized cells for each device. On the other hand, medium- or large-sized devices, such as vehicles, use a medium- or large-sized battery system having a plurality of cells electrically connected with each other because high output and large capacity is necessary for the medium- or large-sized devices.
As the unit cell for the medium- or large-sized battery system is widely used a pouch-shaped secondary cell, which is generally packaged in a battery case made of a laminate sheet consisting of aluminum and polymer resin, and therefore, the mechanical strength of the pouch-shaped secondary cell is not high. For this reason, a plurality of unit cells are mounted in a battery cartridge, where the unit cells are connected in series or parallel, and a plurality of battery cartridges are electrically connected with each other to constitute a battery module.
A battery module widely used for hybrid electric vehicles has a closed structure in which an electrolyte cannot leak from each unit cell (secondary cell). That is to say, the closed type battery module has an advantage of preventing leakage of the electrolyte. However, the closed type battery module has problems in that heat generated in unit cells is accumulated, and the accumulated heat accelerates the deterioration of the cells and that a small or large number of unit cells are overheated when they are operated abnormally, and therefore, the unit cells may catch on fire or explode. Lithium-ion secondary cells or lithium-ion polymer secondary cells, which are currently generating much interest in the potential uses of unit cells, generate heat while the secondary cells are charged and discharged. When such heat is continuously accumulated in the unit cell, the deterioration of the unit cell is accelerated, and furthermore, the unit cell may catch on fire or explode.
The applicant of the present application developed a battery cartridge and a battery module having a novel structure to solve the above-mentioned problems, which have been filed to the Korean Intellectual Property Office and accorded Korean Patent Application No. 2004-111699.
The battery cartridge and the battery module described in the above-mentioned patent application, have several features of stably mounting unit cells having low mechanical strength, effectively removing heat from the unit cells, and preventing the unit cells from overheating when the unit cells are operated abnormally, thereby improving the service life and safety of the unit cells. Also, this battery module can be manufactured generally in a compact structure, and therefore, this battery module is preferably used to provide a small-sized high-output, large-capacity battery module or battery system.
On the other hand, it is required that the electrical connection between the unit cells and the coupling of the unit cells with other components be carried out in a small space so as to manufacture the compact battery module or battery system. As a result, it is possible that short circuits occur, and it is difficult to accomplish mechanical coupling by welding or using bolts and nuts. For this reason, there has been proposed a method of accomplishing the electrical connection between the unit cells in a contact fashion using elastic members, such as springs. In this conventional method, however, the mechanical strength and the resistance to vibrations are low, and the elastic members may easily corrode with the result that the contact resistance is increased. Furthermore, the connected parts are easily separated from each other. These problems also occur at a printed circuit board (PCB), which is mounted to measure the voltage and the temperature of the unit cells.